1. Field of the Invention:
This invention relates to an ultrasonic medical treatment apparatus for use in giving medical treatment to a human body with ultrasonic energy, and more particularly to an applicator for use in such treatment.
2. Description of the Prior Art:
A shock wave type apparatus for destroying calculus (kidney stones) has received practical application. The apparatus utilizes shock wave energy generated by an electric discharge or by explosion. However, in recent years, the use of focused ultrasonic energy to destroy calculuses in a human body has become feasible. This method has become of major interest as a substitute for the utilization of shock wave energy. This is because the use of ultrasonic energy can result in a significant reduction in the size and the manufacturing cost of calculus-destroying apparatus. In addition, such apparatus requires substantially no expendable materials.
The conventional applicator for use in ultrasonic calculus-destroying apparatus has a spherical piezoelectric element that generates ultrasonic energy and concentrates the same on the focal point thereof.
The piezoelectric element type calculus-destroying apparatus usually generates acoustic energy smaller than that generated by an electric discharge shook wave type apparatus, when both have an applicator of the same area. Thus, in order to obtain the necessary acoustic energy, a piezoelectric element having a relatively larger area is required. However, such a piezoelectric element is usually made of ceramics. Thus, the size of a single concave piezoelectric element is inevitably limited. Therefore, a plurality of unit piezoelectric elements are combined so as to form the necessary area in combination.
FIGS. 4a through 4c show conventional applicators manufactured by the combination of unit piezoelectric elements. FIG. 4a shows an applicator formed by combination of plural circular concave piezoelectric elements 1a through 1g, which are all the same size. In this case, there are gaps between adjacent concave elements 1a through 1g. Thus, these gaps decrease the space factor of the applicator. FIG. 4b shows an applicator made by combination of plural hexagonal concave elements 2a through 2g. This applicator has a space factor higher than that of the applicator of FIG. 4a.
However, the outside diameter of this applicator is limited. Moreover, at the center of this applicator, a hole for inserting an imaging ultrasonic probe is often provided. Thus, the space factor of this applicator decreases at the periphery thereof. FIG. 4c shows an applicator provided with auxiliary small-size elements 3a through 3f that fill the periphery thereof. However, in general, the individual elements are respectively connected to plural separate driving circuits. Thus, when plural elements having different surface areas are used, the electrical loads of such driving circuits are varied in proportion to the respective surface areas. Thus, plural driving circuits with specifications different from each other are required. As a result, the apparatus becomes cumbersome and complicated. Moreover, this raises the manufacturing costs thereof.
FIG. 5 shows another conventional ultrasonic medical treatment applicator. In FIG. 5, an ultrasonic medical treatment applicator 4 has a base plate 5. The internal surface of base plate 5 is formed in a spherical configuration. As can be seen from the drawing, a plurality of unit elements 6 of equilateral hexagons are combined and adhere to the base plate 5 so as to constitute the applicator 4. The plural unit elements 6 are fixed such that ultrasonic energy generated from these elements 6 is accurately concentrated on a focal point. Thus, once the unit elements 6 are fixed accurately, the ultrasonic medical treatment applicator 4 functions steadily without being out of focus, and it is free from undesirable dispersion of the ultrasonic energy.
However, as described above, the unit elements 6 are made of ceramics. Thus, these elements 6 are susceptible to damage during the process of manufacturing the applicator 4 or its operation. Actually, it is not a rare case that even when the ultrasonic medical treatment applicator 4 is used, some of unit elements 6 are found to be defective. Such defectives of the unit elements 6 decrease the generation of ultrasonic energy. Moreover, the unit elements 6 are fixed to the base plate 5 so as to be united therewith. Thus, the entire ultrasonic medical treatment applicator 4, per se, must be replaced. Otberwise the maximum performance thereof cannot be completely insured.
As described above, in the conventional ultrasonic medical treatment applicator, there are problems as follows. When plural unit elements identical in size and shape are used, the space factor of the applicator decreases. When plural unit elements with surface areas different from each other are used in combination, the driving circuits therefor become complicated.
Moreover, in the conventional ultrasonic medical treatment applicator, plural unit elements are fixed to the base plate in order that the focuses of these elements invariably coincide with each other. However, this causes disadvantages in that when only a part of the unit elements become defective, the whole applicator must be replaced.